1. Field of Invention
The present invention relates to a projector. More particularly, the present invention relates to a light-guiding apparatus for an illumination system.
2. Description of Related Art
Since optical projectors were developed, they have been applied in many fields. They serve an ever expanding range of purposes, from consumer products to high technology, such as by projecting and displaying enlarged still images or motion pictures of presentations on a projection screen during conferences. However, as projector applications broaden, demands on contrast and brightness of projectors increase. The contrast and brightness of a projector are mostly determined by its illumination system.
FIG. 1 is a schematic view of an illumination system and a guiding apparatus of a conventional illumination system and light-guiding apparatus. In the existing framework of the conventional illumination and guiding apparatus, light emitted from a light source 102 is collected and reflected by an ellipsoidal reflector 104 to pass through a color wheel 106, and then enters a light tunnel 108. An outlet of light tunnel 108 is square-shaped, so light is uniformly emitted from the light tunnel 108 with a square cross section after being reflected many times inside the light tunnel 108.
The square-section light passes through a relay lens 110 composed of several lenses and a light path turning device 112 to arrive at a digital micro-mirror device (DMD) chip 114. The light path turning device 112 in FIG. 1 is a total internal reflection (TIR) prism. An image generated from the DMD chip 114 is turned by the light path turning device 112, and then is projected to a screen 118 by a projection lens 116.
The relay lens 110 in FIG. 1 is a light-guiding apparatus for transmitting light from the light tunnel 108 to the DMD chip 114. The conventional light-guiding apparatus, such as the relay lens 110 composed of several lens, is used to modify the square-section light emitted from the light tunnel 108 to match an incident angle and an effective dimension of the DMD chip 114. The relay lens 110 usually is composed of more than three lenses. However, an aberration of the relay lens 110 itself twists or blurs edges of the square-section light, thus causing the light spot to be irregular. Furthermore, the light from the light source 102 includes many different wavelengths and these different wavelengths of light generate a chromatic aberration while passing through the relay lens 110.
Though the aberrations are reduced by optical designs to improve image quality, the multiple lenses are complicated in design and expensive. In addition, if more lenses are added to the relay lens 110 to compensate for the aberrations, light intensity is unavoidably lost, which lowers the performance of a projector.